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Publication 1790-UM003A-EN-P

Appendix

D

Using Thermocouple Junctions

This appendix describes the types of thermocouple junctions available,
and explains the trade-offs in using them with the thermocouple/mV
analog input module.

Available thermocouple junctions are:

•

grounded

•

ungrounded (isolated)

•

exposed

Using a Grounded
Junction Thermocouple

With a grounded junction thermocouple, the measuring junction is
physically connected to the protective sheath, forming a completely
sealed integral junction. If the sheath is metal (or electrically conductive),
there is electrical continuity between the junction and sheath. The
junction is protected from corrosive or erosive conditions. The response
time approaches that of the exposed junction type described in Using an
Exposed Junction Thermocouple on page D-3.

ATTENTION

!

Take care when choosing a thermocouple junction, and
connecting it from the environment to the module. If you
do not take adequate precautions for a given
thermocouple type, the electrical isolation of the module
might be compromised.

Extension Wire

Metal Sheath

Measuring Junction
Connected to Sheath

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84
85
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87
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»

Summary of Contents for CompactBlock LDX 1790D-4T0

Page 1: ...CompactBlock LDX I O Thermocouple Modules 1790D T4T0 1790D 4T0 1790P T4T0 User Manual AB Drives ...

Page 2: ......

Page 3: ...or the Application Installation and Maintenance of Solid State Control available from your local Allen Bradley office describes some important differences between solid state equipment and electromechanical devices that should be taken into consideration when applying products such as those described in this publication Reproduction of the contents of this copyrighted publication in whole or part ...

Page 4: ...te input and output image words for the module a list of remedies you have already tried processor type and firmware number See the label on the processor hardware types in the system including all I O modules fault code if the processor is faulted Your Questions or Comments on this Manual If you find a problem with this manual please notify us of it on the enclosed How Are We Doing form Phone Uni...

Page 5: ...s 2 2 Hazardous Location Considerations 2 2 Selecting a Location 2 5 Protecting the Circuit Board from Contamination 2 6 Installing CompactBlock LDX I O 2 6 Set the Node Address on the DeviceNet 1790D 4T0 T4T0 Base Block 2 6 Set the Station Address on the 1790P T4T0 PROFIBUS DP Base Block 2 7 Mounting 2 7 Mount the Base Block 2 7 Panel Mounting 2 7 DIN Rail Mounting 2 8 Connect the DeviceNet Cable...

Page 6: ...1790D 4T0 T4T0 3 14 Configure DeviceNet Thermocouple mV Modules Using RSNetWorx 3 15 Chapter Summary 3 19 Chapter 4 Diagnostics and Troubleshooting Safety Considerations 4 1 Indicator Lights 4 1 Activating Devices When Troubleshooting 4 1 Stand Clear of the Equipment 4 2 Program Alteration 4 2 Safety Circuits 4 2 Module Operation vs Channel Operation 4 2 Power up Diagnostics 4 3 Module Status 4 3 ...

Page 7: ... Thermocouples C 11 Type S Thermocouples C 12 Type T Thermocouples C 14 References C 17 Appendix D Using Thermocouple Junctions Using a Grounded Junction Thermocouple D 1 Using an Ungrounded Isolated Junction Thermocouple D 2 Using an Exposed Junction Thermocouple D 3 Appendix E Module Configuration for PROFIBUS Configure PROFIBUS Thermocouple mV Modules 1790P T4R0 E 1 Configure Thermocouple mV Mo...

Page 8: ...Publication 1790 UM003A EN P May 2002 viii ...

Page 9: ...r range detection and indication When configured for thermocouple inputs the module can convert the thermocouple readings into digital temperature readings in C or F When configured for mV inputs the module assumes that the direct mV input signal is linear prior to input to the module The data can be configured on board each module as engineering units x 1 The module uses a digital filter that pro...

Page 10: ...ution Filter set for 10 Hz Accuracy 0 to 55 C Module only B 300 to 1800 C 3000 to 18000 0 1 C 4 2 C E 270 to 1000 C 2700 to 10000 0 1 C 2 5 C J 210 to 1200 C 2100 to 12000 0 1 C 2 8 C K 270 to 1370 C 2700 to 13700 0 1 C 3 3 C R 50 to 1768 C 500 to 17680 0 1 C 3 6 C S 50 to 1768 C 500 to 17680 0 1 C 3 6 C T 270 to 400 C 2700 to 4000 0 1 C 1 3 C N 270 to 1300 C 2700 to 13000 0 1 C 3 1 C Table 1 2 mV...

Page 11: ...Net Module Figure 1 2 1790P T4T0 PROFIBUS DP Module Node Address Switches Module and Network Status Indicators 43223 Thermoucouple mV Channel Indicators Thermocouple mV Connections D sub Connector shown CompactBlock LDX 1790D 8BV8V 8 INPUTS 8OUTPUTS DC POWER 0 7 0 7 DeviceNetNetwork Connection DIN Rail Slot Panel Mount Hole Node Address Switches Module and Network Status Indicators Panel Mount Hol...

Page 12: ...t or PROFIBUS network The 1790D modules also receive 24V dc power through DeviceNet An external 24V dc auxiliary source is required to power the 1790P module and all thermocouple mV channels System Operation At power up the module performs a check of its internal circuits memory and basic functions If no faults are found during power up diagnostics the module status LED is turned on green Once a c...

Page 13: ...device depending upon how you configured the channel When configured for thermocouple input types the module converts the analog input voltages into cold junction compensated and linearized digital temperature readings The module uses the National Institute of Standards and Technology NIST ITS 90 standard for linearization for all thermocouple types J K T E R S B N When configured for millivolt in...

Page 14: ...module sends thermocouple or mV data through the microcontroller to the DeviceNet network The PROFIBUS block diagram is similar Chapter Summary In this chapter you learned about the 1790D 4T0 T4T0 1790P T4T0 thermocouple mV module See Chapter 2 to learn how to install and wire the module ...

Page 15: ...ires external supplies for both system power and for the thermocouple mV channels Table 2 1 1790D 4T0 T4T0 Power Specifications Power Specification DeviceNet Supply voltage 24V dc nominal Voltage range 11 28 8V dc Power dissipation 1 2W maximum 28 8V dc Field Supply voltage 24V dc nominal Voltage range 21 6 26 4V dc 10 Power dissipation 1 5W maximum 26 4V dc Table 2 2 1790P T4T0 Power Specificatio...

Page 16: ...pollution occurs except that occasionally a temporary conductivity caused by condensation shall be expected 2 Over Voltage Category II is the load level section of the electrical distribution system At this level transient voltages are controlled and do not exceed the impulse voltage capability of the product s insulation 3 Pollution Degree 2 and Over Voltage Category II are International Electrot...

Page 17: ...re le plus faible peut être utilisé pour déterminer le code de température global du système Les combinaisons d équipements dans le système sont sujettes à inspection par les autorités locales qualifiées au moment de l installation WARNING EXPLOSION HAZARD Do not disconnect equipment unless power has been removed or the area is known to be nonhazardous Do not disconnect connections to this equipme...

Page 18: ... within an enclosure that is suitably designed for those specific environmental conditions that will be present and appropriately designed to prevent personal injury resulting from accessibility to live parts The interior of the enclosure must be accessible only by the use of a tool Subsequent sections of this publication may contain additional information regarding specific enclosure type ratings...

Page 19: ... which generate significant radiated heat In addition route shielded twisted pair wiring away from any high voltage I O wiring ATTENTION Preventing Electrostatic Discharge This equipment is sensitive to electrostatic discharge which can cause internal damage and affect normal operation Follow these guidelines when you handle this equipment Touch a grounded object to discharge potential static Wear...

Page 20: ... are explained in detail in the following procedures for both the 1790D 4T0 T4T0 DeviceNet and 1790P T4T0 PROFIBUS DP modules Set the Node Address on the DeviceNet 1790D 4T0 T4T0 Base Block Each base block comes with its internal program set for node address 63 To reset the node address adjust the switches on the front of the block The two switches are most significant digit MSD and least signific...

Page 21: ...g the block Panel Mounting 1 Place the block against the panel where you want to mount it 2 Gently pull and position the expansion cover to the left 3 Place a center punch nail or similar device through the mounting holes in the block and make two marks on the panel lower left and upper right corners of the module 4 Remove the block and drill two holes in the panel to accommodate each of the mount...

Page 22: ...ly in place DIN Rail Mounting 1 Hook the top slot of the block over the DIN Rail 2 Pull down on the locking lever while pressing the block against the rail 3 Push up on the locking lever to secure the block to the rail when the block is flush against the rail CompactBlock LDX 1790 16BVOX EXPANSION UNIT 16 INPUTS DCPOWER 0 7 0 7 41 mm 1 6 in 95 mm 3 74 in Expansion Cover 43242 Locking Lever f 43243...

Page 23: ...5 pin micro male connector with locking screws Connect the DeviceNet wiring drop line to one of the DeviceNet connectors as shown below A color coded wiring diagram is also printed next to the connector on the left side of the module WARNING If you connect or disconnect the DeviceNet cable with power applied to this module or any device on the network an electrical arc can occur This could cause a...

Page 24: ...s shown in the following table WARNING If you connect or disconnect the PROFIBUS cable with power applied to this module or any device on the network an electrical arc can occur This could cause an explosion in hazardous location installations Be sure that power is removed or the area is nonhazardous before proceeding Table 2 3 Wiring Descriptions for 9 Pin D Sub Connector Pin Number Name Descript...

Page 25: ...ach it to the base block as shown below Use the locking screws on the connector to fasten it to the base block Connect Power to the 1790P T4T0 Block To apply power to the block refer to the above illustration 43249 PROFIBUS Connector Green GND Black COM Red 24V dc Module Power Connector underneath module AB Drives ...

Page 26: ... right angles If multiple power supplies are used with analog millivolt inputs the power supply commons must be connected Terminal Block Do not use the module s NC terminals as connection points For millivolt sensors use Belden 8761 shielded twisted pair wire or equivalent to ensure proper operation and high immunity to electrical noise For a thermocouple use the shielded twisted pair thermocouple...

Page 27: ... additional details If it is necessary to connect the shield drain wire at the module end connect it to earth ground using a panel or DIN rail mounting screw Refer to Industrial Automation Wiring and Grounding Guidelines Allen Bradley publication 1770 4 1 for additional information Noise Prevention To limit the pickup of electrical noise keep thermocouple and millivolt signal wires as far as possi...

Page 28: ...f the wire 3 At one end of the cable twist the drain wire and foil shield together bend them away from the cable and apply shrink wrap Then earth ground at the preferred location based on the type of sensor you are using See Grounding on page 2 13 ATTENTION To prevent shock hazard care should be taken when wiring the module to analog signal sources Before wiring any module disconnect power from th...

Page 29: ... D Using Thermocouple Junctions for additional information on wiring grounded ungrounded and exposed thermocouple types IMPORTANT When using an ungrounded thermocouple the shield must be connected to ground at the module end 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 24V NC NC NC CH0_A CH0_B CH1_A CH1_B NC NC CH2_A CH2_B CH3_A CH3 B NC NC ...

Page 30: ...rature temperature at the module s terminal junction between the thermocouple wire and the input channel must be compensated for Cold junction compensating thermistors have been integrated in the module Chapter Summary In this chapter you learned how to install and wire your modules See Chapter 3 to learn about module data status and channel configuration with DeviceNet ...

Page 31: ...odule Memory Map The module uses five input words for data and status bits input image Figure 3 1 Memory Map Input Image The input image file represents data words and status words Input words 0 through 3 hold the input data that represents the value of the analog inputs for channels 0 through 3 These data words are valid only when the channel is enabled and there are no errors Input word 4 holds ...

Page 32: ...Data Table Word Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 Thermocouple Input Data Channel 0 1 Thermocouple Input Data Channel 1 2 Thermocouple Input Data Channel 2 3 Thermocouple Input Data Channel 3 4 Not Used S11 S10 S9 S8 Not Used S3 S2 S1 S0 Table 3 2 Input Data Table Word Decimal Bit Description Read Word 0 Bits 00 15 Channel 0 input data Read Word 1 Bits 00 15 Channel 1 input data Read Wor...

Page 33: ...ta to the actual temperature values for the selected thermocouple type per NIST ITS 90 standard It expresses temperatures in 0 1 degree units either C or F depending on which temperature scale is selected For mV inputs the module expresses voltage in 10uV units Negative temperatures are returned in 16 bit two s complement binary format See Appendix B for a detailed explanation of two s complement ...

Page 34: ...e time Effects of Filter Frequency on Noise Rejection The filter frequency that you choose for the module determines the amount of noise rejection for the inputs A smaller filter frequency e g 10Hz provides the best noise rejection and increases effective resolution but also increases channel update time A larger filter frequency e g 500 Hz provides lower noise rejection but also decreases the cha...

Page 35: ...put signal are passed with 3 dB of attenuation The following table shows cutoff frequencies for the supported filters All frequency components at or below the cutoff frequency are passed by the digital filter with less than 3 dB of attenuation All frequency components above the cutoff frequency are increasingly attenuated as shown in the following graphs for several of the input filter frequencies...

Page 36: ... 80 100 120 140 160 180 200 20 0 40 60 80 100 120 140 160 180 200 20 0 40 60 80 100 120 140 160 180 200 20 0 40 60 80 100 120 140 160 180 200 20 3 dB 1300 0 1150 750 500 250 65 5 Hz 900 3 dB 3000 0 2500 1500 1000 500 131 Hz 2000 10 Hz Input Filter Frequency 60 Hz Input Filter Frequency 250 Hz Input Filter Frequency 500 Hz Input Filter Frequency Frequency Hz Frequency Hz Frequency Hz Frequency Hz G...

Page 37: ...or no jitter due to noise and is used in defining the effective resolution The following graphs provide the effective resolution for each thermocouple type for each available filter frequency These graphs do not include the affects of unfiltered input noise Choose the frequency that most closely matches your system requirements Figure 3 3 Type B Thermocouple Table 3 7 Effective Resolution vs Input...

Page 38: ...Publication 1790 UM003A EN P 3 8 Module Data Status and Channel Configuration for DeviceNet Figure 3 4 Type E Thermocouple Figure 3 5 Type J Thermocouple ...

Page 39: ...Publication 1790 UM003A EN P Module Data Status and Channel Configuration for DeviceNet 3 9 Figure 3 6 Type K Thermocouple Figure 3 7 Type R Thermocouple AB Drives ...

Page 40: ...Publication 1790 UM003A EN P 3 10 Module Data Status and Channel Configuration for DeviceNet Figure 3 8 Type S Thermocouple Figure 3 9 Type T Thermocouple ...

Page 41: ... an external CJC Entering an estimated temperature may be the least accurate way for CJC compensation Using external CJC is the most expensive way Using the compensation built into the module provides the easiest way for CJC Built in module cold junction linearization may be enabled or disabled If enabled the proper cold junction compensation value will be applied to the thermocouples If disabled ...

Page 42: ...mined from the combination of the module and the thermocouple The total error is the sum of the following module accuracy and error due to temperature thermocouple error error due to thermocouple lead wire CJC error Module and Temperature Error The combined module error and error due to ambient temperature is shown in the table below Table 3 8 Module Update Time Filter Frequency Module Update Time...

Page 43: ...rnal CJC or the estimated cold junction value Table 3 10 Thermocouple Error Thermocouple Type Useable Range C Standard Tolerance Error Whichever error factor is greater Special Tolerance Error B 870 to 1700 0 5 0 25 E 0 to 900 200 to 0 1 7 C or 0 5 1 7 C or 1 1 C or 0 4 1 C or 0 5 J 0 to 750 2 2 C or 0 75 1 1 C or 0 4 K 0 to 1250 200 to 0 2 2 C or 0 75 2 2 C or 2 1 1 C or 0 4 NA R 0 to 1450 1 5 C ...

Page 44: ... files you need to configure the modules go to the following Website http www ab com networks eds EDS files for blocks with matching catalog numbers for D Shell and terminal block versions are the same Thus on the website or in RSNetWorx for DeviceNet there may be only one catalog number listed for both versions When using 3rd party configuration software simply load the EDS files into the softwar...

Page 45: ...hermocouple mV Modules Using RSNetWorx Following the steps below to configure 1790D 4T0 T4T0 thermocouple mV modules 1 Open RSNetWorx for DeviceNet 2 Using the selections on the left of the window below construct you system If your network is up just click on the Online Browse button Online Browse Button AB Drives ...

Page 46: ...ar to the following appears Thermocouple mV modules will have parameters similar to the following Click the device Parameters tab to display the screen in which you can set parameters If you see a lock next to an entry this indicates that you cannot change that parameter On this screen you see all the parameters for the module These include Autobaud temperature units filter frequency cold junction...

Page 47: ...uency Thermocouple mV Input type Cold Junction Compensation Enable Manual Offset Value and Autobaud Select the desired temperature units in degrees C or F and notch filter frequency ALL four channels will be configured identically Select the thermocouple mV input type for each channel from the dropdown list Select to have Autobaud either Enabled or Disabled AB Drives ...

Page 48: ... If built in CJC is disabled you can enter a constant cold junction offset value The value is always entered in C The range is 0 to 70 C 000 to 700 70 C is entered as 700 158 F as 700 also Once module configuration is complete click either the Download or Apply button and click Yes for the popup question Then click OK to close the module properties window ...

Page 49: ...e Groups checkbox b Close the No Group Specified folder c Open the I O Input Values and I O Input Status folders d Click the Monitor button The module parameters are sequentially updated Chapter Summary In this chapter you learned how to setup and configure your module See Chapter 4 to learn how to troubleshoot using the module indicators Click the Monitor button Check Groups Open these folders Cl...

Page 50: ...Publication 1790 UM003A EN P 3 20 Module Data Status and Channel Configuration for DeviceNet ...

Page 51: ...mportance The following sections describe several safety concerns you should be aware of when troubleshooting your control system Indicator Lights When the green MOD and NET LED on the thermocouple module are illuminated it indicates that power is applied to the module that it has passed its internal tests and that the module is communicating on the network Activating Devices When Troubleshooting ...

Page 52: ...easons like over travel limit switches stop push buttons and interlocks should always be hard wired to the master control relay These devices must be wired in series so that when any one device opens the master control relay is de energized thereby removing power to the machine Never alter these circuits to defeat their function Serious injury or machine damage could result Module Operation vs Cha...

Page 53: ... 1790D 4T0 T4T0 1790P 4T0 LED Indicator Status Description Module Status Solid Red Unrecoverable fault Flashing Red Recoverable fault Solid Green Normal operation OK Flashing Green Standby Off No power Table 4 2 1790D 4T0 T4T0 LED Descriptions LED Indicator Status Description Network Status Solid Red Unrecoverable communication fault Flashing Red Recoverable communication fault Solid Green Communi...

Page 54: ...ible causes for an out of range condition include The temperature is too hot or too cold for the type of thermocouple being used The wrong thermocouple is being used for the input type selected or for the configuration that you have programmed The input device is faulty The signal input from the input device is beyond the scaling range Open Circuit Detection On each scan the module performs an ope...

Page 55: ...nput channel 0 bit 01 corresponds to input channel 1 and so on When set 1 the input signal if below the input channel s minimum range Bits 04 07 Not used Set to 0 Bit 08 11 Overrange for individual channels Bit 08 corresponds to input channel 0 bit 09 corresponds to input channel 1 and so on When set 1 the input signal if above the input channel s maximum range or open thermocouple is detected Bit...

Page 56: ...Publication 1790 UM003A EN P 4 6 Diagnostics and Troubleshooting ...

Page 57: ...8 2 6 Test Fc Operating Shock Operating Non operating I0g 30g IEC60068 2 27 Test Ea Unpackaged Shock ES 002 Emissions Group 1 Class A CISPR 11 ESD Immunity 8kV air discharges IEC 61000 4 2 Radiated RF Immunity 10V m with 1kHz sine wave 80 AM from 80MHz to 1000MHz 10V m with 200Hz 50 Pulse 100 AM 900Mhz IEC 61000 4 3 EFT B Immunity 1kV 5kHz on power ports 2kV 5kHz on signal ports 2kV 5kHz on commun...

Page 58: ...cations Network Protocol PROFIBUS DP EN50170 Communication of the slave with a Class 1 master Communication of the slave with a Class 2 master Redundancy Not supported Repeater Control Signal RS485 signal Implementation Type DPC31 Freeze Mode Supported Sync Mode Supported Auto Baud Rate Supported Fail Safe Mode Supported Station Type Slave FMS Support Not supported Indicators 1 red green module st...

Page 59: ...ns ODVA ODVA conformance tested to ODVA DeviceNet specifications 2 See the Product Certification link at www ab com for Declarations of Conformity Certificates and other certification details DeviceNet Power Supply voltage 24V dc nominal Voltage range 11 28 8V dc Power dissipation 1 2W maximum 28 8V dc PROFIBUS Power Supply voltage 24V dc nominal Voltage range 19 2 28 8V dc Power dissipation 2W ma...

Page 60: ...K 270 to 1370 C 2700 to 13700 R 50 to 1768 C 500 to 17680 S 50 to 1768 C 500 to 17680 T 270 to 400 C 2700 to 4000 N 270 to 1300 C 2700 to 13000 Resolution 16 bits 0 1 C bit or 0 1 F bit Thermocouple Sensors 20bit Sigma Delta modulation converter Data Format 16 bit Integer 2 s compliment Module Scan Time 140ms channel Notch Filter 60Hz Overall accuracy 0 2 Full scale 0 C 55 C Settable Notch Filter ...

Page 61: ...A 0 indicates a value of 0 a 1 indicates the decimal value of the position The equivalent decimal value of the binary number is the sum of the position values Positive Decimal Values The far left position is always 0 for positive values As indicated in the figure below this limits the maximum positive decimal value to 32767 all positions are 1 except the far left position For example 0000 1001 000...

Page 62: ... positions In the figure below all positions are 1 the value is 32767 32768 1 For example 1111 1000 0010 0011 214 213 212 211 25 21 20 215 16384 8192 4096 2048 32 2 1 32768 30755 32768 2013 1 x 2 2 1 x 2 1 1 x 2 16384 1 x 2 8192 1 x 2 4096 1 x 2 2048 1 x 2 1024 1 x 2 128 1 x 2 512 1 x 2 256 1 x 2 64 1 x 2 32 1 x 2 16 1 x 2 8 1 x 2 4 1 x 2 32768 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 14 13 12 11 10 9 8 7 ...

Page 63: ... the temperature scale especially in the temperature range from t68 630 74 C to 1064 43 C where the type S thermocouple was the standard interpolating device on the IPTS 68 For additional technical information regarding ITS 90 refer to the NIST Monograph 175 Type B Thermocouples This section discusses Platinum 30 percent Rhodium Alloy Versus Platinum 6 percent Rhodium Alloy thermocouples commonly ...

Page 64: ...on content appears to be the most suitable material for the purpose Type B thermocouples should not be used in reducing atmospheres nor those containing deleterious vapors or other contaminants that are reactive with the platinum group metals 42 unless suitably protected with nonmetallic protecting tubes They should never be used in metallic protecting tubes at high temperatures The Seebeck coeffi...

Page 65: ...id helium temperatures 4 2 K although their Seebeck coefficient becomes quite low only about 2mV C at 4K Both thermoelements of type E thermocouples have a relatively low thermal conductivity good resistance to corrosion in moist atmospheres and reasonably good homogeneity For these three reasons and their relatively high Seebeck coefficients type E thermocouples have been recommended 8 as the mos...

Page 66: ...nor differences in heat treatment provided that the treatment does not violate any of the restrictions mentioned above For most general applications they may be used with the heat treatment given by the wire manufacturers However when the highest accuracy is sought additional preparatory heat treatments may be desirable in order to enhance their performance Details on this and other phases of the ...

Page 67: ...ls of carbon chromium copper manganese nickel phosphorus silicon and sulfur Thermocouple wire represents such a small fraction of the total production of commercial iron wire that the producers do not control the chemical composition to maintain constant thermoelectric properties Instead instrument companies and thermocouple fabricators select material most suitable for the thermocouple usage The ...

Page 68: ...dized type above 760 C If type J thermocouples are taken to high temperatures especially above 900 C they will lose the accuracy of their calibration when they are recycled to lower temperatures If type J thermocouples are used in air at temperatures above 760 C only the largest wire AWG 8 3 3 mm should be used and they should be held at the measured temperature for 10 to 20 minutes before reading...

Page 69: ... the NBS Cryogenics Division showed that the type K thermocouple may be used down to liquid helium temperatures about 4K but that its Seebeck coefficient becomes quite small below 20K Its Seebeck coefficient at 20K is only about 4µV K being roughly one half that of the type E thermocouple which is the most suitable of the letter designated thermocouples types for measurements down to 20K Type KP a...

Page 70: ...ll increase in the iron content accompanied by a slight decrease in the manganese and cobalt contents ASTM Standard E230 87 in the 1992 Annual Book of ASTM Standards 7 specifies that the initial calibration tolerances for type K commercial thermocouples be 2 2 C or 0 75 percent whichever is greater between 0 C and 1250 C and 2 2 C or 2 percent whichever is greater between 200 C and 0 C In the 0 C ...

Page 71: ...4K but that its Seebeck coefficient becomes very small below 20K Its Seebeck coefficient at 20K is about 2 5µV K roughly one third that of type E thermocouples which are the most suitable of the letter designated thermocouples types for measurements down to 20K Nevertheless types NP and NN thermoelements do have a relatively low thermal conductivity and good resistance to corrosion in moist atmosp...

Page 72: ... in stainless steel Their studies showed that the thermoelectric instabilities of such assemblies increase rapidly with temperature above 1000 C It was found also that the smaller the diameter of the sheath the greater the instability Additionally thermocouples sheathed in Inconel showed substantially less instability above 1000 C than those sheathed in stainless steel Bentley and Morgan 52 stress...

Page 73: ...ive RN thermoelement is commercially available platinum that has a nominal purity of 99 99 percent 21 An industrial consensus standard ASTM E1159 87 specifies that rhodium having a nominal purity of 99 98 percent shall be alloyed with platinum of 99 99 percent purity to produce the positive thermoelement which typically contains 13 00 0 05 percent rhodium by weight This consensus standard 21 descr...

Page 74: ...e to the user It does not apply to thermocouples having compacted mineral oxide insulation Type S Thermocouples This section describes Platinum 10 percent Rhodium Alloy Versus Platinum thermocouples commonly known as type S thermocouples This type is often referred to by the nominal chemical composition of its positive SP thermoelement platinum 10 percent rhodium The negative SN thermoelement is c...

Page 75: ...metallic protection tube for use at high temperatures The stability of type S thermocouples at high temperatures 1200 C depends primarily upon the quality of the materials used for protection and insulation and has been studied by Walker et al 25 26 and by Bentley 29 High purity alumina with low iron content appears to be the most suitable material for insulating protecting and mechanically suppor...

Page 76: ...cent whichever is greater between 0 C and 1450 C Type S thermocouples can be supplied to meet special tolerances of 0 6 C or 0 1 percent whichever is greater The suggested upper temperature limit 1480 C given in the ASTM standard 7 for protected type S thermocouples applies to AWG 24 0 51 mm wire This temperature limit applies to thermocouples used in conventional closed end protecting tubes and i...

Page 77: ... thermoelements apply to both types of thermoelements over the temperature range recommended for each thermocouple type However if should not be assumed that type TN and type EN thermoelements may be used interchangeably or that they have the same commercial initial calibration tolerances The low temperature research 8 by members of the NBS Cryogenics Division showed that the type T thermocouple m...

Page 78: ... in composition under thermal neutron irradiation The copper in the thermoelements is converted to nickel and zinc Because of the high thermal conductivity of type TP thermoelements special care should be exercised when using the thermocouples to ensure that the measuring and reference junctions assume the desired temperatures ASTM Standard E230 87 in the 1992 Annual Book of ASTM Standards 7 speci...

Page 79: ... 03 Philadelphia ASTM 1992 102 230 8 Sparks L L Powell R L Hall W J Reference tables for low temperature thermocouples Natl Bur Stand U S Monogr 124 1972 June 61p 9 Starr C D Wang T P Effect of oxidation on stability of thermocouples Proceedings of the American Society for Testing and Materials Vol 63 1185 1194 1963 10 Roeser W F Dahl A I Reference tables for iron constantan and copper constantan ...

Page 80: ...ls Vol 63 1185 1194 1963 19 Bentley R E Short term instabilities in thermocouples containing nickel based alloys High Temperatures High Pressures 15 599 611 1983 20 Kollie T G Horton J L Carr K R Herskovitz M B Mossman C A Temperature measurement errors with type K Chromel vs Alumel thermocouples due to short ranged ordering in Chromel Rev Sci Instrum 46 1447 1461 1975 21 ASTM American Society for...

Page 81: ...ai M Sakurai H Pokhodun A I Moiseeva N P Perevalova S A de Groot M J Zhang J Fan K Wu S New reference functions for platinum 10 rhodium versus platinum type S thermocouples based on the ITS 90 Part I and Part II in Temperature Its Measurement and Control in Science and Industry Vol 6 Schooley J F ed New York American Institute of Physics 1992 537 546 29 Bentley R E Changes in Seebeck coefficient o...

Page 82: ...d Control Systems 106 107 March 1972 38 Burns G W Gallagher J S Reference tables for the Pt 30 percent Rh versus Pt 6 percent Rh thermocouple J Res Natl Bur Stand U S 70C 89 125 1966 39 Ehringer H Uber die lebensdauer von PtRh thermoelementen Metall 8 596 598 1954 40 Acken J S Some properties of platinum rhodium alloys J Res Natl Bur Stand U S 12 249 RP650 1934 41 Hendricks J W McElroy D L High te...

Page 83: ...on R L Lyons J D Kollie T G Christie W H Eby R Decalibration of sheathed thermocouples Temperature Its Measurement and Control in Science and Industry Vol 5 Schooley J F ed New York American Institute of Physics 1982 977 1007 52 Bentley R E Morgan T L Ni based thermocouples in the mineral insulated metal sheathed format thermoelectric instabilities to 1100 C J Phys E Sci Instrum 19 262 268 1986 53...

Page 84: ...ators 16 89 100 1989 59 Bentley R E Irreversible thermoelectric changes in type K and type N thermocouple alloys within nicrosil sheathed MIMS cable J Phys D 22 1908 1915 1989 60 Bentley R E Thermoelectric behavior of Ni based ID MIMS thermocouples using the nicrosil plus sheathing alloy Temperature Its Measurement and Control in Science and Industry Vol 6 Schooley J F ed New York American Institu...

Page 85: ... a completely sealed integral junction If the sheath is metal or electrically conductive there is electrical continuity between the junction and sheath The junction is protected from corrosive or erosive conditions The response time approaches that of the exposed junction type described in Using an Exposed Junction Thermocouple on page D 3 ATTENTION Take care when choosing a thermocouple junction ...

Page 86: ...tive sheath made of electrically insulated material for example ceramic An alternative is to float the metal sheath with respect to any path to chassis ground or to another thermocouple metal sheath Thus the metal sheath must be insulated from electrically conductive process material and have all connections to chassis ground broken Note that a floated sheath can result in a less noise immune ther...

Page 87: ...mocouple wires unprotected against corrosive or mechanical damage As shown in the next illustration using an exposed junction thermocouple can result in removal of channel to channel isolation Isolation is removed if multiple exposed thermocouples are in direct contact with electrically conductive process material Measuring Junction Isolated from Sheath Measuring Junction with No Sheath IN 0 IN 3 ...

Page 88: ... exposed junction thermocouples do not allow the measuring junctions to make direct contact with electrically conductive process material Preferably use a single exposed junction thermocouple with multiple ungrounded junction thermocouples Consider using all ungrounded junction thermocouples instead of the exposed junction type ...

Page 89: ...ve resolution module update time Configure PROFIBUS Thermocouple mV Modules 1790P T4R0 Configuration of the 1790P T4T0 thermocouple mV modules is accomplished through PROFIBUS configuration software with easy to use GSD files To obtain the GSD files you need to configure the module access the following website http www ab com networks gsd The example in this chapter shows you how to configure the ...

Page 90: ...rary to open the pane If the on line Browse pane is closed choose 4 View On line to open the pane You should now be ready to set up your system 5 Expand the Master and Slaves folders in the PROFIBUS Device pane 6 Choose the Master device for your network drag and drop the device to the Network pane From the following window Expand Master folder Expand Slave folder Choose Master for your network dr...

Page 91: ...aves from the PROFIBUS Device pane 2 Dragging and dropping them to the network pane Or if online by performing a search for slaves See the following screens for an outline of this procedure Choose the Master communication parameters First configure the network search properties Second search for slave modules AB Drives ...

Page 92: ...ou dragged and dropped from the PROFIBUS Device pane you must set the station number 8 Click the SLC address tab for data size information and to set the I O data type For this example we choose I Type Input Image in the processor Highlight the slave right click the mouse and select GSD Files 1790P T4T0 gsd Station number should be set Highlight and drag and drop the slave device to the Network pa...

Page 93: ...its filter frequency cold junction compensation enable manual offset and input thermocouple mV type The 1790P T4T0 module produces 5 words of data The produced 5 words will appear in the processor input data table On this screen you see all the parameters for the module These include watchdog time temperature units filter frequency cold junction compensationenable manual offset and input thermocou...

Page 94: ...elect the filter cutoff frequency desired All four channels will be configured identically Select to enable auto or disable manual built in cold junction compensation If built in CJC is disabled you can enter a constant cold junction offset value The value is always entered in C The range is 0 to 70 C 000 to 700 70 C is entered as 7000 158 F as 700 also ...

Page 95: ... and location to save your configuration 3 Click Save This saves your project as a pbc PROFIBUS configuration file Download the Configuration To download the configuration 1 Verify that the processor is in Program Mode 2 Make sure the serial communication cable is connected between the PC comm port and the scanner serial port 3 Highlight Master in the Network pane Select the thermocouple mV input ...

Page 96: ...e Edit Connect You may be prompted with a message indicating a configuration mismatch between what is in the scanner and your current PROFIBUS project In this case select Yes to retain your configuration Any configuration mismatches display for the Master status Highlight the Master and then right click to select Connect ...

Page 97: ...e following message displays Card is online Do you want to load configuration Select Yes to load your new configuration You may receive this message This is only a warning that if your Min Cycle Time is not twice as long as the Scan Time then you may lose serial communications This message can usually be ignored unless you require online monitoring The Master status now changes to the Configured P...

Page 98: ...m LED on the scanner The connection should report OK The master should now display Summary This appendix illustrated how to configure your PROFIBUS thermocouple mV module with the SST PROFIBUS Configuration tool For more information consult your PROFIBUS network documentation PROFIBUS scanner documentation and network configuration tool documentation ...

Page 99: ...a device s differential voltage gain to common mode voltage gain Expressed in dB CMRR is a comparative measure of a device s ability to reject interference caused by a voltage common to its input terminals relative to ground CMRR 20 Log10 V1 V2 common mode voltage The voltage difference between the negative terminal and analog common during normal differential operation common mode voltage range T...

Page 100: ... representing the ideal analog input An analog input is composed of a series of input values corresponding to digital codes For an ideal analog input the values lie in a straight line spaced by inputs corresponding to 1 LSB Linearity is expressed in percent full scale input See the variation from the straight line due to linearity error exaggerated in the example below LSB Least significant bit Th...

Page 101: ...ability The closeness of agreement among repeated measurements of the same variable under the same conditions resolution The smallest detectable change in a measurement typically expressed in engineering units e g 1 C or as a number of bits For example a 12 bit system has 4096 possible output states It can therefore measure 1 part in 4096 sampling time The time required by the A D converter to sam...

Page 102: ...Publication 1790 UM003A EN P G 4 ...

Page 103: ...LED indicator operation 4 5 channel status LED 1 4 channel step response 3 4 3 5 channel update time 3 5 definition G 1 circuit board protecting 2 6 CJC See Cold Junction Compensation CMRR See common mode rejection ratio Cold Junction Compensation 1 4 2 16 3 11 built in CJC 3 11 error 3 13 estimated temperature 3 11 external CJC 3 11 comments about manual iv common mode 3 4 common mode rejection d...

Page 104: ... and channel cutoff frequency 3 5 and channel step response 3 5 and noise rejection 3 4 definition G 2 frequency response graphs 3 6 frequency See filter frequency full scale definition G 2 full scale range definition G 2 G general diagnostic features 1 4 general specifications A 3 grounding 2 13 H hardware features 1 3 general diagnostic features 1 4 hazardous location considerations 2 2 heat con...

Page 105: ...ion G 2 multiplexing 1 5 mV analog input signal types 1 2 mV device compatibility 1 2 N negative decimal values B 2 network status 4 3 noise 3 4 noise rejection 3 4 normal mode rejection definition G 3 number of significant bits definition G 3 O open wire detection 4 4 operation system 1 4 out of range detection 4 4 overall accuracy definition G 3 over range flag bits 3 3 overview 1 1 general desc...

Page 106: ...12 T technical support See support iv temperature error 3 12 terminal blocks wiring 2 15 thermistors 2 16 thermocouple analog input signal types 1 2 compatibility 1 2 descriptions C 1 error 3 13 exposed junction D 3 grounded junction D 1 junction types D 1 lead wire error 3 13 Type B description C 1 effective resolution graph 3 7 Type E description C 3 effective resolution graph 3 8 Type J descrip...

Page 107: ...Publication 1790 UM003A EN P May 2002 I 5 W wire type 2 14 wiring 2 1 guidelines 2 12 modules 2 14 routing considerations 2 5 terminal blocks 2 15 AB Drives ...

Page 108: ...Publication 1790 UM003A EN P May 2002 I 6 ...

Page 109: ...you Completeness all necessary information is provided 1 2 3 Can we add more information to help you procedure step illustration feature example guideline other explanation definition Technical Accuracy all provided information is correct 1 2 3 Can we be more accurate text illustration Clarity all provided information is easy to understand 1 2 3 How can we make things clearer Other Comments You ca...

Page 110: ...E NECESSARY IF MAILED IN THE UNITED STATES BUSINESS REPLY MAIL FIRST CLASS MAIL PERMIT NO 18235 CLEVELAND OH POSTAGE WILL BE PAID BY THE ADDRESSEE 1 ALLEN BRADLEY DR MAYFIELD HEIGHTS OH 44124 9705 PLEASE FASTEN HERE DO NOT STAPLE PLEASE REMOVE ...

Page 111: ...AB Drives ...

Page 112: ...Publication 1790 UM003A EN P May 2002 2 PN 957657 67 Copyright 2002 Rockwell Automation All rights reserved Printed in the U S A ...

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